This invention relates to centrifugal fans and centrifugal fan systems, and particularly to those for commercial application.
In the past, in the era of low cost energy, it was not uncommon to simply ignore the fact that in industrial applications, the system's volume requirements varied from time to time. A constant rpm motor was simply allowed to run at its rated speed with the cost of doing so borne by the user.
With the advent of an increase in energy cost, and for other reasons, there has been more emphasis in recent years for fan systems wherein the rated capacity of a centrifugal fan could be varied to match the volume of air required by the system, to thereby achieve a horsepower reduction. While there are a number of ways of approaching this problem, three have been most often utilized. In one set up, a variable speed drive is interposed between the motor and the centrifugal fan itself, so while the motor is operating at a constant speed, the fan operates at a variable one. This is not wholly satisfactory because of the cost of the variable speed drive itself and the cost of maintaining it.
Another solution is to make use of the improvements in variable speed electrical motors, and particularly AC inverter motors. They enable the electrical motor to be driven at a variable speed in accordance with the volume demands of the system. However, they are expensive.
The third approach is to allow the motor to operate at a constant speed, but to provide dampers or vanes in front of the inlet cone. This means that the rated capacity of the fan depends on the position of the vanes. This does achieve a reduction in horsepower, but the fans are noisy.